This application is a U.S. national phase application based on International Application No. PCT/SE01/00331, filed Feb. 15, 2001; which claims priority from Swedish Application No. 0000456-4, filed Feb. 18, 2000.
The present intention relates to an arrangement for cleaning, airflow control and for pushing away Melt from the opening of the airport in incineration boilers. The invention can preferably be applied for the abovementioned functions in principally but not exclusively the lower primary air ports in recovery boilers which are used for the chemical recovery process in paper pulp manufacture.
From U.S. Pat. No. 3,742,916, an arrangement, marketed under the name RODDINGMASTER(copyright), for cleaning and airflow control in air ports on boilers is previously known, in which cleaning and airflow control are brought about by a regulating and scraping sleeve which can be drawn in and out in the air port. Here, the sleeve is located on an essentially horizontally arranged regulating rod actuated by a regulating cylinder which is arranged outside the boiler and has a relatively large space requirement outside the recovery boiler.
The air regulation is effected by virtue of the fact that an annular gay is formed around the sleeve and the walls of the surrounding air port, which gap is imparted an increasing flow cross section when the sleeve is drawn out in the air port away from the recovery boiler. The flow cross section is closed when the sleeve has been pushed in towards the opening of the air port level with the wall of the recovery boiler, where the cleaning function is brought about when the edges or the sleeve scrape against the inner walls of the air port.
A disadvantage of this construction is that the air supply to the boiler is formed in an annular gap around the sleeve, which results in relatively weak penetration of the air jet into the boiler. For complete incineration of material supplied, it is of the utmost importance that the air which is supplied to the combustion process is distributed uniformly over the entire cross section of the boiler. The efficiency of the combustion process is absolutely vital in order for it to be possible to reduce emissions of inter alia NOx and CO and to minimize the risk of melt and liquor drops being carried off from the combustion chamber with the flue gases.
U.S. Pat. No. 3,875,904, U.S. Pat. No. 3,943,861 and U.S. Pat. No. 4,027,604 disclose further detailed improvements of the RODDINGMASTER(copyright) concept, namely sealing of the rear end of the sleeve, a common actuator for a number of sleeves and, respectively, telescopic regulating rods for the sleeve.
Regulating devices for air supply and integrated cleaning for airports of recovery boilers have formed the subject of a number of inventions. U.S. Pat. No. 4,653,409 and U.S. Pat. No. 5,070,023 disclose regulating devices with a cleaning function, in which the regulating cylinders are arranged essentially horizontally.
U.S. Pat. No. 4,583,552, U.S. Pat. No. 4,838,182 and U.S. Pat. No. 4,846,080 disclose variants in which the cleaning function is brought about via pivotable scrapers that can be swung out of the way so that they do not disrupt the airflow, These complicated mechanical solutions are, however, quite unsuitable for recovery boilers where there is a risk of the mechanisms being jammed by the environment of splashing melt.
U.S. Pat. No. 4,099,471 and U.S. Pat. No. 5,528,999 disclose other variants in which sliding sleeves for the cleaning function have been provided with pivotable dampers acting counter to the airflow through the interior of the sleeve in these constructions also, the dampers are exposed to melt splash and thus the risk of the damper function being jammed.
U.S. Pat. No. 4,545,308 and U.S. Pat. No. 4,940,004 disclose air port constructions which are intended to provide maximum penetration of the air jet and in which the inlet itself to the boiler is given a narrow nozzle-shaped design. These solutions mean, however, that the regulating body itself has to be drawn out very far from the wall opening in order for a substantial flow to be developed, as a result of which there is a considerable space requirement around the boiler.
The prior art has suffered from one or more disadvantages with regard to:
the space requirement around the boiler for the regulating equipment,
a large regulating stroke for regulating between minimum and maximum airflow,
a complicated mechanical constructions not suitable for the environment,
a poor degree of penetration of the air jet brought about by the regulating device,
a limited possibility of, in the same regulating device, also being able to push away slag from the air inlet in the event of a high level of melt in the boiler.
The object of the invention is to bring about air control and cleaning of of the airport using one and the same mechanism, in which the air control is carried out in order to maintain in a simple manner the degree of penetration of the air that is supplied to the furnace of the boiler.
Another object is to make it possible for the combustion air to be supplied better over the entire cross section of the boiler, at the same time as the time the combustion gases remain in the boiler can be kept relatively long, which results in better combustion and reduction of the risk of liquor drops and melt being carried off from the combustion chamber with the flue gases.
At the same time, when the invention is applied in the lower air ports, an improved possibility can be obtained for pushing melt/slag away from the air port in the event of a high melt level.
In a preferred embodiment, the arrangement is arranged so that it occupies less space outside the boiler than constructions that are already in existence/use. The invention also brings about three-fold functionality with a minimum number of components which results in a very cost-effective solution.
Another object is that the construction is to be robust and not to have complicated mechanisms that risk becoming locked if they ate exposed to splash from the melt.
A further object is for it to be possible for the airflow to be adjusted more rapidly with a small regulating movement. By means of the invention, airflow regulation, cleaning and pushing away melt/slag can be achieved at the lowest possible coat and with great operational safety.